Automatic volume control



R. HILDEBRANDT y fi AUTOMATIC VOLUME CONTROL Filed Sept. 29. 1958 7'0.SVG/VA L SOURCE 7'0 PLA 7E CIRCUIT 7'0 AUDIO DETECTOR INVEN TOR. RA/ RHIL DEBRANDT BY v /gfg I A TORN E Y.

Patented June 18, 1940 Parser ()FFiCE AUTOMATIC VOLUME CONTROL ticn ofGermany Application September 29, 1938, Serial No. 232,254 In GermanySeptember 14, 1937 9 Claims.

It is known in the art that volume control means may be usedsimultaneously in both the radio and the audio parts of a receiverapparatus. This insures the advantage that such fluctuations of theaverage radio frequency. amplitude as may still remain after regulationin. the radio portion will be compensated so that a practically constantand stable output potential is obtained. Because of the high audioamplitude, however, distortions will be unavoidable with the use of whatis known in the prior art as grid potential regulation as applied to atube of the exponential characteristic type. As a matter of fact,special designs of tube would be required in this case.

According to the invention a receiver comprising volume control means inboth the radio and the audio parts is designed in such a way that thefading control in the audio portion is negative feedback.

The invention offers the advantage that, on the one hand, upon receptionof transmitter stations of average and great power or field intensity, 5the audio portion operates under conditions free from distortions,while, on the other hand, in case of reception of Weak stations, therearises no reduction of sensitiveness of the set as a result of the factthat the negative feedback, or antiregeneration, has been reduced. Inother words, the advantage of the distortion-corrective action of thenegative feed-back is utilized particularly in the case when the same isneeded, while the shortcoming inherent in the reduction of gain isremoved particularly when it is troublesome. In other words, the meritsand demerits of negative feedback are utilized under most favorableconditions. Contradistinct thereto, in unvaried negative feedbackschemes the distortions of a receiver which substantially arise in theaudio portion, to be sure, are markedly diminished, though they tend toprevent at the same time from receiving feeble stations because of thereduction of the gain.

The outstanding feature of the invention. could also be expressed bystating that the amount of equalization, or correction, of distortion inthe audio portion is adapted to the intensity of the incoming field sothat it is rendered operative particularly for the stronger stations andthus for stations that are mostly heard. Inasmuch as the regulation ofthe negative feedback in the audio portion because of the dependence ofthis action upon the average carrier amplitude exer- 5 cises at the sametime a volume control action,

accomplished by regulation of the value of a the scheme moreover insuresthe advantage of assuring a stable output potential.

If the negative feedback is so designed that the high frequencies aresubject to a reduced negative feedback action, there results at the sametime a variation of the band-width. For it will be noted that when apowerful station is coming in, the negative feedback action is operativeso that the high frequencies which have been slighted, for instance, inthe radio portion are emphasized with a resultant great breadth of theaudio band, While in the reception of feeble transmitters the negativefeedback is nearly ineffective so that the high frequencies will not befavored.

Volume control in the radio portion is accomplishable in well knownmanner by means of grid-voltage regulation. However, it. is alsopossible to effect volume control by regulation of negative feedbackeffected in the radio part with audio energy. However, the essentialcharacteristic of the invention resides in the regulated negativefeedback in the audio partinasmuch as it is in the latter where maximumdistortions arlse.

Figs. 1 and 2 show different embodiments of the invention. Fig. 1illustrates a regulating rectifier G for radio signals which regulatesthe grid biasing voltage of an RF amplifier tube H. The negativefeedback potential in the audio portion, for instance, is taken offacross the output transformer T and impressed upon the oathoderesistance K of the AF tube N preceding the last. Included in one of thenegative feedback leads is a resistance R such as a glow-lamp which is afunction of the current, the said resistance being traversed by theanode or plate current J (or the cathode current or screen-grid current)of the regulated or AVG-controlled tube H. As a result, the intensity ofthe negative feedback is influenced. Upon reception of a weaktransmitter station, as will be noted, the plate current J is regulatedupwards so that the resistance of the glow-lamp increases with theresult that a lower portion of the negative feedback potential arisesacross the resistance K.

Referring to Fig. 2 it will be seen that the negative feedback ordegenerative relation is insured only inside the last stage of thereceiver in that the negative feedback potential is divided between theresistances R, W, and K and then impressed upon the grid of the powertube. R in this scheme is a temperature dependent resistance such asuranium dioxide resistance which is heated from the heater winding Hwhich is traversed by the plate currents J of the regulated tubes. Thereare other embodiments conceivable for the basic idea of the invention,for instance, in which an electron tube is utilized for the regulated orcontrolled resistance R, as is well known in the prior art.

What is claimed is:

1. In a radio receiver provided with at least one signal carriertransmission tube, a detector and an audio frequency network, meansproviding degenerative feedback of audio voltage from a later point inthe audio network to an earlier point thereof, means responsive tosignal carrier amplitude variation for controlling the gain of thetransmission tube, and means responsive to variation in space currentflow of the controlled tube for controlling the magnitude of saiddegenerative feedback.

2. In a radio receiver provided with at least one signal carriertransmission tube, a detector and an audio frequency network, meansproviding degenerative feedback of audio Voltage from a later point inthe audio network to an earlier point thereof, means connected to saiddetector, responsive to signal carrier amplitude variation, forcontrolling the gain of the transmission tube, and means responsive tovariation in space current flow of the controlled tube for controllingthe magnitude of said degenerative feedback.

3. In a radio receiver provided with at least one signal carriertransmission tube, a detector and an audio frequency network, meansproviding degenerative feedback of audio voltage from a later point inthe audio network to an earlier point thereof, means, responsive tosignal carrier amplitude variation, for controlling the gain of thetransmission tube, and temperature-depend ent resistance meansresponsive to variation in space current fiow of the controlled tube forcontrolling the magnitude of said degenerative feedback.

4. In a radio receiver provided with at least one signal carriertransmission tube, a detector and an audio frequency network, meansproviding degenerative feedback of audio voltage from a later point inthe audio network to an earlier point thereof, means, responsive tosignal carrier amplitude variation, for controlling the gain of thetransmission tube, and means common to the space current path of thecontrolled tube and said feedback means, and responsive to variation inspace current flow of the controlled tube,

for controlling the magnitude of said degenerative feedback.

5. In a signal carrier reception system including a carrier energytransmission network and an audio amplifier circuit, a circuit connectedbetween two successive points of the audio circuit for feeding backaudio voltage, and means connected to said carrier network andresponsive to signal carrier amplitude variation for automaticallyadjusting the magnitude of the feedback voltage.

6. In a signal carrier reception system including a carrier energytransmission network and an audio amplifier circuit, a circuit connectedbetween two successive points of the audio circuit for feeding backaudio voltage in degenerative phase, and temperature-dependent meansconnected to said carrier network and responsive to signal carrieramplitude variation for automatically adjusting the magnitude of thefeedback voltage,

'7. In a modulated carrier reception system of the type including acarrier amplifier, a demodulator and a modulation amplifier, the methodwhich includes degeneratively feeding back modulation voltage from themodulation amplifier output to its input, deriving a direct currentvoltage from the amplified carrier energy which varies directly with thecarrier amplitude, ap-

plying the direct current voltage to the carrier amplifier in again-reducing sense as the carrier amplitude increases, and controllingthe magnitude of said feedback, in response to the variation of thecarrier amplifier space current, in a sense such as to increase feedbackas the carrier amplitude increases.

8. In combination with at least two cascaded signal transmission tubes,a signal feedback path between the output and input of the second tube,and means, including an element in the space current path of said firsttube, for controlling the magnitude of signal feedback in response tothe amplitude variation of the signal.

9. In an audio-modulated carrier receiver of the type provided with anaudio amplifier, means for providing degenerative audio feedback betweentwo successive points of the-amplifier, and. means responsive solely tothe carrier amplitude variation for automatically adjusting themagnitude of said feedback.

RAINER. HILDEBRANDT.

